Conventionally, a noninvasive living body measuring device which measures components such as hemoglobin and the like in blood by imaging a living body using an imaging means and analyzing blood vessels in the image of the living body, is disclosed in U.S. Patent Application Publication No. 2004-162471. The device disclosed in U.S. Patent Application Publication No. 2004-162471 is provided with a first light source for irradiating blood vessels (veins) in the wrist of a user, a light-receiving unit for detecting optical information from the blood vessels irradiated by the first light source, and an analyzing unit for analyzing the blood components flowing through the blood vessels based on the optical information. Thus, the user is able to continuously measure the components contained in blood simply by mounting the device on the wrist.
When measuring the components in blood using the device disclosed in U.S. Patent Application Publication No. 2004-162471, a band is mounted on the arm of the user nearer the heart than the wrist and the arm is pressurized with a predetermined pressure in order to facilitate imaging of the blood vessels. Thus, the blood flow of the wrist region is blocked and the blood vessels (veins) of the wrist expand.
When pressure is applied to the living body by the band, not only the target blood vessel but also the capillaries of the peripheral tissue around the target blood vessel are congested with blood. In the measurement of the components in blood, the amount of components in blood are determined based on the difference between the degree of brightness of the blood vessel and the degree of brightness of the surrounding area of the blood vessel in a captured image of the living body that includes the blood vessel. However, there may be only a small difference in the degrees of brightness when the surrounding tissues are congested with blood by the application of the pressure. Therefore, there is a problem that the measured value is smaller than the actual value.
Accordingly, the device disclosed in U.S. Patent Application Publication No. 2004-162471 is provided with a second light source for illuminating the surrounding tissue of the blood vessel in addition to the first light source, and a second light-receiving unit for detecting an optical information from the living tissue irradiated by the second light source, and the amount of the components in blood is corrected based on the optical information from the living tissue.
However, in the device disclosed in U.S. Patent Application Publication No. 2004-162471, a special light source and light-receiving unit are required to obtain the optical information from the living tissue surrounding the blood vessel in addition to the mechanism for obtaining optical information from the blood vessel which is the primary measurement target. Thus, the structure of the device becomes more complex. Furthermore, analysis of the components in blood takes time since the living body is not able to be imaged during the acquisition and analysis of the optical information from the living tissue surrounding the blood vessel.
Besides, the device of U.S. Patent Application Publication No. 2004-162471 is further provided with a third light source for illuminating the blood vessel by irradiating light in the same direction as that of the first light source, and the above mentioned light-receiving unit detects the optical information from the blood vessel illuminated by the first and third light sources. That is, the device of U.S. Patent Application Publication No. 2004-162471 is a reflective type device in which the light sources and imaging means are situated on one side of the living body. Since the light source is not able be disposed within the visual field of the imaging means in such a reflective type device, a uniform brightness within the visual field of the imaging means is difficult to achieve. Therefore, the light intensity from the first and third light sources has a great effect on the measurement accuracy. For this reason, it is important to adjust the light intensity from the first and third light sources in this reflective type noninvasive living body measuring device.